DynVar is an international working group on the modelling of the dynamics and variability of the stratosphere-troposphere system, part of SPARC (activity website here). DynVar focuses on the interactions between atmospheric variability, dynamics and climate change, with a particular emphasis on the two-way coupling between the troposphere and the stratosphere. To this end, DynVar promotes the development and use of coupled atmosphere-ocean-seaice general circulation models, with the atmospheric component extending to above the stratopause. The key questions addressed by the activity are:

•How do dynamical processes contribute to persistent model biases in the mean state and variability of the atmosphere, including biases in the position, strength, and statistics of blocking events, storm tracks and the stratospheric polar vortex?

•How does the stratosphere affects climate variability at intra-seasonal, inter-annual and decadal time scales?

•What is the role of dynamics in shaping the climate response to anthropogenic forcings (e.g. global warming, ozone depletion) and how do dynamical processes contribute to uncertainty in future climate projections?

DynVar has been active in the assessment of the stratosphere mean climate, variability and change and of the stratosphere-troposphere dynamical coupling in the climate models that participated in the latest set of climate projections, carried out under the fifth Coupled Model Inter-comparison Project (CMIP5). On discerning the role of the stratosphere on intraseasonal time scales, initiatives within DynVar analyses the stratospheric seasonal prediction hindcasts produced as part of WGSIP's Stratosphere Historical Forecast Project (SHFP).

The use of simplified models and more theoretical approaches to build the knowledge of two-way stratosphere-troposphere coupling is also an important component of the activity. DynVar is as well extending its focus to tropospheric dynamics, storm tracks, jets, blocking and their modes of variability, with the aim of reaching a comprehensive understanding of the troposphere-stratosphere system variability and change. These activities within DynVar connect most closely to the WCRP Grand Challenges on Clouds, Circulation, and Climate Sensitivity and Near-term Climate Prediction.